The present invention relates to record track following and seeking, particularly to improved patterns plus apparatus for utilizing such patterns for both track following and seeking.
In magnetic data recorders, particularly of the rotating disk type, high track densities, i.e., densities greater than 500 tracks per inch (tpi), require electronic servo controls for precisely positioning recording and sensing transducers with respect to a given record track. This is achieved by two modes of operation. First, the track to be accessed must be first located. This action is termed "track seeking" and is achieved by relatively moving the transducer with respect to the record member in a direction transverse to the length of the tracks until the appropriate track is located. Once the track is located, a second mode of operation, called "track following", keeps the transducer centered as close as possible on the track being accessed.
In a multidisk recorder, one of the disk surfaces is reserved for containing such servo patterns whereby a so-called "comb" head assembly can move radially of the record disk for accessing record or data tracks on the other record surfaces. In other disk recorders, where only a single disk surface is accessed at a given time and employing a transducer assembly designed to operate with but a single disk surface, the luxury of a separate servo signal disk surface is not available. In those situations, so-called "sector servoing" is employed, such as taught by Sippel, supra. In these latter systems, sector patterns, i.e., positioning information signals, are interleaved betweeen data signals such that as the record member relatively passes the sensing transducer, positioning and data signals are alternately sensed by the transducer. This arrangement enables the transducer to be automatically and precisely positioned with respect to the record track being accessed.
While the above-stated actions on their face appear simple and straightforward, as track density increases in order to create a greater storage capacity per disk surface, locating a record track from a plurality of record tracks on a random basis becomes an exceedingly difficult proposition. This is particularly true if one desires to servo position the recording transducer directly to the track to be accessed without overshoot plus a successful track access on each and every try. An additional problem arises in that, as the track widths are decreased and the track pitch (center-to-center spacing of adjacent tracks) is decreased, the position indicating or servo signals have correspondingly less amplitude. This means that the amplitude of the readback signal becomes smaller and more unpredictable. That is, the servo signals become more susceptible to dropouts, transducer-to-record-surface spacing variations, and intermodulation in the transducer of signals detected from two adjacent record tracks. The above-identified problems are magnified when flexible record media are employed. Further, the substances of flexible record disks exhibit such dimensional instability that position indicating servo signals and the information signals must be on the same disk, at least at higher recording densities (track density in particular).
Accordingly, it is desired to provide rapid track acquisition and precise following. All of the above should be achieved at minimum cost because of the competitive nature of record storage apparatus.
Another important factor is the reliable detection and evaluation of the positioning or servo signals received by the servo apparatus. Such servo apparatus should exhibit a maximal tolerance to amplitude variations, intermodulation perturbations, record track eccentricities, and yet be fully responsive to signals indicating a position error signal with respect to positioning a transducer with respect to a record track.